The furnace ignitor lights then goes out is a common HVAC issue that can leave a home without heat and raise safety concerns. This article explains why an ignitor lights then goes out, how professionals diagnose the problem, practical troubleshooting steps, and when to call a qualified technician. It focuses on reliable, safety-first approaches for homeowners and technicians in the United States.
| Symptom | Likely Causes | Typical Fixes |
|---|---|---|
| Ignitor Sparks Or Glows Then Flame Fails | Faulty gas valve, blocked burner, weak flame rollout or flame sensor | Clean burners, test/replace gas valve, inspect flame sensor |
| Ignitor Clicks Rapidly Then Stops | Ignition control module fault, transformer or wiring issue | Test control board/transformer, repair wiring, replace module |
| Ignitor Glows Then Shuts Off Without Spark | Gas supply interruption, pressure issue, limit switch tripping | Check gas supply, inspect pressure/venting, service limit switch |
How Modern Furnaces Ignite Fuel
Most modern gas furnaces use one of three ignition systems: hot surface ignitors (HSI), intermittent pilot (direct spark) ignition, or standing pilot (older models). In an HSI system the ignitor glows, heating to ignition temperature to light burners. In spark ignition a control module sends sparks to light the gas. A standing pilot uses a continuously burning small flame. A symptom where the furnace ignitor lights then goes out generally involves HSI or spark systems and indicates a failure in the ignition sequence or a safety device interrupting the process.
Common Reasons The Furnace Ignitor Lights Then Goes Out
1. Faulty Flame Sensor
The flame sensor confirms burners are lit; if it’s dirty or failing it may not detect flame, causing the control board to shut off gas for safety. Dirty sensors are a frequent cause when the ignitor lights then goes out immediately after flame appears.
2. Weak Or Intermittent Gas Supply
Low gas pressure, partially closed valves, or utility interruptions can prevent burners from sustaining a flame. The ignitor may perform normally, but the flame fails to establish or drops out when pressure is insufficient.
3. Faulty Ignition Control Board Or Module
The control board orchestrates the ignition sequence. If the module is intermittently failing, it may stop energizing the gas valve after the ignitor lights, causing the system to shut down as a protective measure.
4. Bad Gas Valve Or Solenoid
Gas valves have solenoid coils that open the gas flow during ignition. A valve that sticks or a solenoid that loses continuity can result in the ignitor lighting but burners not remaining lit.
5. Blocked Burners Or Dirty Orifices
Debris or corrosion on burners interferes with proper flame formation. The ignitor may glow correctly, but a disrupted flame pattern causes poor flame sensing and shutdown.
6. Venting, Pressure Switch, Or Inducer Problems
Modern furnaces use pressure switches and inducer fans to ensure safe venting. A failed pressure switch, clogged vent, or weak inducer can cause the furnace to abort ignition after the ignitor lights.
7. Limit Switch Or Thermal Cutoff Tripping
If a high-limit switch triggers from overheating or airflow issues, the furnace may stop mid-sequence. This can result in the ignitor lighting then going out as the system prevents unsafe operation.
Safety Checks Before Troubleshooting
Prioritize safety: turn off power to the furnace and shut off the gas if work requires access to burners or gas components. Only homeowners comfortable with electrical and gas systems should perform basic checks. If any uncertainty exists, contact a licensed HVAC technician or the gas utility.
Step-By-Step Troubleshooting Guide
Visual And Simple Checks
Confirm thermostat is set to heat and temperature is above the call point. Inspect for error codes on the furnace control board or LED status lights and record blinking patterns for diagnosis. Ensure the gas valve at the furnace and the main supply are open.
Inspect And Clean The Flame Sensor
Turn off power and open the furnace to access the flame sensor. Remove and gently clean using fine-grit sandpaper or emery cloth to remove oxidation. Reinstall and test. A cleaned flame sensor often resolves the ignitor lights then goes out symptom.
Check Burners And Ignitor Condition
Inspect burners for rust, debris, or misalignment. Ensure the hot surface ignitor is intact without cracks. Replace cracked or brittle HSIs; they may glow but fail under load. For spark systems, verify spark gap and electrode condition.
Test Gas Pressure And Valve Operation
A licensed technician should test manifold pressure and verify gas valve operation. An easy homeowner check is ensuring other gas appliances operate normally. If other appliances show low flame, contact the utility or a pro.
Evaluate Venting And Pressure Switch Function
Inspect exhaust vent for obstructions like nests or snow. Listen for inducer fan operation during startup. A non-spinning inducer or pressure switch that doesn’t close will interrupt ignition after the ignitor lights.
Inspect Control Board And Wiring
Look for obvious wiring damage, burnt connectors, or swollen capacitors on the control board. Verify the ignitor gets proper voltage during the sequence. Replace the ignition control module if diagnostics point to intermittent failures.
When To Call A Professional
Call a licensed HVAC technician if any of these apply: gas odor, suspected gas leak, cracked ignitor, persistent ignition failures after basic cleaning, wiring or control board issues, low gas pressure, or if the homeowner is uncomfortable with gas/electrical work. Professionals have tools like manometers, multimeters, and pressure gauges to diagnose and repair safely.
Common Repairs And Typical Costs
Repair costs vary by region and system type. Typical U.S. ranges: flame sensor cleaning or replacement $75–$200, hot surface ignitor replacement $100–$400, gas valve replacement $300–$800, control board $200–$700, inducer motor $250–$700. Exact prices depend on labor rates and part brands.
Preventive Maintenance To Avoid Future Ignition Problems
- Annual Tune-Ups: Schedule professional maintenance including burner cleaning, sensor inspection, and safety control testing.
- Change Filters Regularly: Replace filters every 1–3 months to maintain airflow and prevent limit trips.
- Keep Vents Clear: Keep exhaust and intake vents free of debris, snow, and vegetation.
- Address Rust And Corrosion: Replace corroded burners or components promptly to prevent ignition failures.
Troubleshooting Checklist For Technicians
- Verify thermostat call for heat and power to furnace.
- Record LED error codes and sequence timing.
- Test continuity and voltage to ignitor and gas valve.
- Inspect flame sensor reading and clean/replace.
- Test gas manifold pressure and valve operation under load.
- Check inducer fan operation and pressure switch response.
- Replace failed ignition control modules or solenoids as needed.
Frequently Asked Questions
Can A Furnace Ignitor Be Tested Without Replacement?
Yes. An HSI can be tested with a multimeter to measure resistance and with a power-on test to ensure it reaches operating temperature. However, visible cracks or brittleness warrant replacement.
How Long Do Ignitors And Flame Sensors Typically Last?
Hot surface ignitors typically last 3–10 years depending on cycles and electrical stress. Flame sensors often last longer but can fail sooner due to deposits or corrosion. Regular maintenance extends life.
Is It Safe To Keep Trying To Relight A Furnace When The Ignitor Keeps Shutting Off?
No. Repeated attempts may flood the combustion chamber with unburned gas or stress components. If the ignitor lights then goes out repeatedly, the unit should be shut down and inspected by a professional.
Key Takeaways For Homeowners
If The Furnace Ignitor Lights Then Goes Out, the most common culprits are a dirty flame sensor, weak gas supply, faulty control module, or burner/venting issues. Homeowners can perform safe checks like cleaning the flame sensor and inspecting vents, but any gas-related diagnosis or repair should be handled by a licensed technician. Regular maintenance is the best defense against ignition failures.
For persistent problems or safety concerns, contact a certified HVAC professional or the local gas utility. Accurate diagnosis prevents unnecessary part replacements and ensures safe, reliable furnace operation.